We report a theoretical study on three tridentate Ir(III) complexes for organic light-emitting diode (OLED) applications. The geometries, electronic structures, emission properties, and quantum efficiencies of these Ir(III) complexes [(C^N^N)Ir((III))(C^N^N)](+) (denoted as 1 hereafter), [(C^N^N)Ir((III))(N^C^N)](+) (2), and [(N^C^N)Ir((III))(N^C^N)](+) (3) were investigated theoretically, where C^N^N = 6-phenyl-2,2'-bipyridine, N^C^N = 2,6-pyridyl-benzene. The ground- and excited-state geometries were optimized at the PBE0/LanL2DZ;6-31G* and uPBE0/LanL2DZ;6-31G* level of theory, respectively, within acetonitrile solvent simulated by PCM. The emission bands and singlet-triplet transition properties of 1 and 2 are well reproduced with TD-PBE0//Stuttgart;cc-pVTZ;cc-pVDZ level of theory. The quantum efficiencies of 1 and 2 that were obtained upon metallic character analysis are comparable with the observed efficiencies. The metallic character analysis also revealed that the theoretically designed isomer 3 would highly phosphorescent at 510 nm.